As a biomagnetic measurement system as medical equipment, for example, a magnetoencephalography system is known. The magnetoencephalography system is a system which accurately examines an active region and the degree of activity in the brain by externally measuring a weak magnetic field generated by neurons.
A biomagnetic measurement system of this type includes a high-sensitivity magnetic measurement apparatus. As this high-sensitivity magnetic measurement apparatus, a SQUID (Superconducting Quantum Interference Device) is used, which can detect a weak biological vector magnetic field such as brain magnetism. However, a cryogenic environment is required for the operation of this device.
On the other hand, as a high-sensitivity magnetic field measurement apparatus which can operate in a room temperature atmosphere, a diamond crystal containing nitrogen-vacancy pairs has been proposed (see, for example, non-patent document 1).
Non-patent document 1 (S. Steinert, F. Dolde, P. Neumann, A. Aird, B. Naydenov, G. Balasubramanian, F. Jelezko, and J. Wrachtrup; “High sensitivity magnetic imaging using an array of spins in diamond”, Review of Scientific Instrument 81, 043705-1 to 5 (2010)) discloses the following contents. Green laser light is used as a blue-green light source which applies exciting light to a diamond crystal as a sensor for measuring a magnetic field, and a CCD array is used to detect a red fluorescence output from the diamond crystal. A magnetic field is measured from the minimum fluorescence intensity value of the microwave frequency dependence of the red fluorescence intensity obtained by sweeping the frequency of microwaves applied to the diamond crystal.
In addition, for example, non-patent document 2 (R. Igarashi, Y. Yoshinari, H. Yokota, T. Sugi, F. Sugihara, K. Ikeda, H. Sumiya, S. Tsuji, I. Mori, H. Tochio, Y. Harada, M. Shirakawa; “Real-time background-free selective imaging of fluorescent nanodiamonds in vivo”, Nano Letters nl302979, October 2012, pp 5726-5732.) discloses a technique of observing a fluorescence output from a single nitrogen-vacancy pair using an SIP (Selective Imaging Protocol) technique. The SIP technique is a technique of removing background noise containing fluorescence other than fluorescence from nitrogen-vacancy pairs by selectively measuring only red fluorescence from nitrogen-vacancy pairs.